KR20230164165A - Grain-oriented electrical steel sheet - Google Patents

Abstract

We provide grain-oriented electrical steel sheets that achieve both low core loss and low distortion with excellent transformer characteristics. A grain-oriented electrical steel sheet has a thermal deformation region extending linearly in a direction transverse to the rolling direction, and in the strain distribution of the thermal deformation region in the rolling direction, the strain at both ends of the thermal deformation region is the thermal deformation region. It is a tensile strain greater than the strain at the center of the region.

Description

Grain-oriented electrical steel sheet

The present invention relates to a grain-oriented electrical steel sheet suitable as an iron core material for transformers and the like.

Grain-oriented electrical steel sheets are used, for example, as materials for iron cores of transformers. In such a transformer, it is necessary to suppress energy loss and noise. The energy loss is influenced by the iron loss of the grain-oriented electrical steel sheet, and the noise is influenced by the magnetostrictive characteristics of the grain-oriented electrical steel sheet.

Particularly in recent years, from the viewpoint of energy conservation and environmental regulations, there has been a strong demand for reduction of energy loss in transformers and noise during operation of transformers. Therefore, it has become very important to develop grain-oriented electrical steel sheets with good core loss and magnetostrictive properties.

Here, the iron loss of the grain-oriented electrical steel sheet mainly consists of hysteresis loss and eddy current loss. Methods for improving hysteresis loss include highly orienting the (110) [001] orientation, called the GOSS orientation, in the rolling direction of the steel sheet, and reducing impurities in the steel sheet. Additionally, methods for improving eddy current loss include increasing the electrical resistance of the steel sheet by adding Si and applying film tension in the rolling direction of the steel sheet, etc. have been developed.

However, when pursuing additional low iron loss of grain-oriented electrical steel sheets, these methods have manufacturing limitations.

Therefore, magnetic domain refinement technology has been developed as a method to pursue additional low iron loss in grain-oriented electrical steel sheets. Magnetic domain refinement technology refers to the introduction of non-uniformity in magnetic flux into a steel sheet after final annealing or baking of an insulating film by physical methods such as forming grooves or introducing local strain, thereby forming a 180° magnetic flux along the rolling direction. This is a method of reducing iron loss, especially eddy current loss, of grain-oriented electrical steel sheets by subdividing the width of the magnetic domains (main magnetic domains).

For example, Patent Document 1 discloses a technology for improving the iron loss from 0.80 W/kg or more to 0.70 W/kg or less by introducing linear grooves with a width of 300 μm or less and a depth of 100 μm or less on the surface of the steel sheet. .

In addition, Patent Document 2 discloses the magnetic flux density of the steel sheet when excited with a magnetizing power of 800 A/m by irradiating a plasma flame in the width direction of the surface of the steel sheet after secondary recrystallization and introducing thermal strain locally ( B ₈ ) is 1.935 T, the maximum magnetic flux density is 1.7 T, and a method of improving the iron loss (W _17/50 ) when excited at a frequency of 50 Hz to 0.680 W/kg is disclosed.

Additionally, the method of introducing linear grooves as disclosed in Patent Document 1 is called heat-resistant magnetic domain refining because the magnetic domain refining effect is not lost even if strain relief annealing is performed after forming the iron core. On the other hand, in the method of introducing thermal strain as disclosed in Patent Document 2, the effect of introducing thermal strain is not obtained by strain removal annealing, so it is called non-heat-resistant magnetic domain refining.

Here, in heat-resistant magnetic domain refining, linear grooves are provided to the steel sheet, and it is known that this treatment deteriorates the permeability of the steel sheet. On the other hand, in non-heat-resistant magnetic domain refining, local strain is introduced into the steel sheet, so deterioration of permeability does not occur as in heat-resistant magnetic domain refining. Therefore, in transformers using laminated iron cores that do not require annealing in the manufacturing process, steel sheet materials subjected to non-heat-resistant magnetic domain refinement are generally used.

Additionally, non-heat-resistant magnetic domain refinement can significantly reduce eddy current loss by introducing strain into the steel sheet. On the other hand, it is known that non-heat-resistant magnetic domain refinement causes deterioration of hysteresis loss, deterioration of magnetostriction, etc. due to the introduction of such strain.

Therefore, for the development of grain-oriented electrical steel sheets with superior core loss and magnetostriction characteristics than before, and further, for the development of transformers with superior energy loss and noise characteristics than before, optimization of the strain introduction pattern during non-heat-resistant magnetic domain refinement is required. It is becoming.

In response to this requirement, in modern grain-oriented electrical steel sheets, a significant improvement in iron loss is realized by applying a combination of the above-mentioned techniques, especially high orientation and magnetic domain refinement, to the steel sheets.

Japanese Patent Publication No. 6-22179 Japanese Patent Publication No. 7-192891

However, the iron loss after the grain-oriented electrical steel sheet manufactured in this way is processed into a transformer increases in building factor (hereinafter also referred to as BF) due to the influence of high orientation, resulting in the problem that the low core loss characteristics of the material cannot be fully utilized. there was. In addition, BF is the ratio of the iron loss of the transformer to the iron loss of the electrical steel sheet material, and the closer the value is to 1, the better the iron loss in the transformer.

One of the factors that increases BF is the rotational core loss at the joint between electrical steel sheets that occurs when assembled as a transformer. This rotational iron loss refers to the iron loss that occurs in the electrical steel sheet material when a rotating magnetic flux having a major axis in the rolling direction is applied.

Since the grain-oriented electrical steel sheet has highly integrated magnetization directions in the rolling direction, when a rotating magnetic flux having a long axis in the rolling direction is applied as described above, a very large loss (rotating iron loss) occurs. In particular, in the transformer iron core, such rotating magnetic flux is generated at the junction.

In contrast, the iron loss of the electrical steel sheet material is the iron loss when an alternating magnetic field having a magnetization component is applied only in the rolling direction. Therefore, when assembled as a transformer, if the rotating iron loss of the electrical steel sheet material is large, the core loss of the transformer increases relative to the iron loss of the electrical steel sheet material, that is, BF increases.

Therefore, in order to improve the building factor of the transformer, it is necessary to reduce rotational core loss, that is, to facilitate rotation of magnetization.

In non-heat-resistant magnetic domain refining, for example, an energy beam is irradiated to the surface of a steel sheet after final annealing or after baking an insulating film, and thermal strain is locally introduced. At this time, compressive stress with respect to the rolling direction remains at the point where the energy beam is irradiated in the direction intersecting the rolling direction. That is, in a grain-oriented electrical steel sheet in which crystal grains with the GOSS orientation (110) [001], which is the easy magnetization axis, are integrated in the rolling direction, when compressive stress acts in the rolling direction due to the introduction of thermal strain, it follows the magnetoelastic effect. , magnetic domains (reflux magnetic domains) having a magnetization direction are formed in the sheet width direction (direction perpendicular to the rolling direction).

Additionally, the magnetoelastic effect refers to the effect that when tensile stress is applied to a grain-oriented electrical steel sheet, the direction of the tensile stress becomes energetically stable, and when compressive stress is applied, the direction perpendicular to the compressive stress becomes energetically stable.

Since the closed magnetic domain formed in this way has a magnetization component in a direction perpendicular to the rolling direction, it is possible to improve the rotational core loss and is advantageous for improving the building factor.

However, it has been revealed that introducing thermal strain to form a freewheeling magnetic domain simultaneously causes an increase in magnetostriction, that is, an increase in transformer noise.

Therefore, in order to achieve both improvement in building factor and lower noise than before, it is necessary to develop a new strain introduction pattern that effectively suppresses the increase in magnetostriction and building factor.

The present invention was made in consideration of the above circumstances, and its purpose is to provide a grain-oriented electrical steel sheet that has excellent transformer characteristics and achieves both low core loss and low distortion.

The inventors conducted intensive studies to achieve the above-mentioned purpose.

First, a review was conducted on ways to improve rotational core loss, which causes an increase in building factor.

As a result, in addition to the formation of the above-described looping magnetic domains, the rotational iron loss can be improved by forming magnetic domains (hereinafter also referred to as auxiliary magnetic domains) with magnetization components in a direction different from the rolling direction when a rotating magnetic field is applied. It turned out that Additionally, it has been found that such auxiliary magnetic domains are likely to be formed starting from regions with locally high magnetostatic energy, such as defects and strains.

Next, in a steel sheet material subjected to non-heat-resistant magnetic domain refinement, a study was conducted on the desirable distribution of the area forming such auxiliary magnetic domains. Candidates for points forming the auxiliary magnetic domain described above at the time of review are shown in FIG. 1.

Candidates could include the inside of the closure domain (I), the end of the closure domain (II), and the region between the irradiation lines (III).

Among these candidates, since the closure magnetic domain (I) has already been formed, the contribution to the improvement of the rotational iron loss due to the formation of the auxiliary magnetic domain is small.

In addition, in the region (III) between the irradiation lines, the rotational iron loss is improved, but there is a risk of magnetostriction and hysteresis loss being deteriorated due to an increase in the amount of deformation. Moreover, since a new process of irradiating the energy beam is required in addition to the process of irradiating the energy beam across the rolling direction, it is also undesirable from a manufacturing standpoint.

In contrast, the closure domain end (II) can eliminate the same concerns as in case (III) above, and since an auxiliary magnetic domain is formed outside the closure domain, an improvement in rotational iron loss can be expected.

Additional studies were conducted on the strain distribution for making this looped domain end (II) the core of the point forming the auxiliary magnetic domain.

Hereinafter, the experimental results that led to completion of the present invention will be described.

A steel strip of grain-oriented electrical steel sheet with a sheet thickness of 0.23 mm manufactured by a known method was irradiated with an electron beam having a ring-shaped or Gaussian-shaped beam profile at different outputs as an energy beam to form a thermal deformation region (magnetic domain segmentation processing). At this time, an electron beam with a beam diameter of 300 μm was used. Here, a beam having a ring-shaped beam profile means a beam having two peaks when the beam profile is acquired by scanning in an arbitrary direction on the two-dimensional plane on which the beam is scanned. A schematic diagram of this beam profile is shown in Figure 2.

A portion of the grain-oriented electrical steel sheet after irradiation with such an electron beam was cut out, and magnetic flux density (B ₈ ) and iron loss (material iron loss: W _17/50 ) were measured as magnetic properties using the single-plate magnetic measurement method described in JIS C2556.

Additionally, a three-phase laminated transformer (iron core weight 500 kg) is manufactured from the above steel strip, and at a frequency of 50 Hz, the iron loss when the magnetic flux density of the iron core leg portion is 1.7 T (transformer iron loss: W _17/50 (WM) ) was measured. The transformer iron loss W _17/50 (WM) at 1.7 T and 50 Hz was taken as the no-load loss measured using a watt meter. From this value of W _17/50 (WM) and the value of W _17/50 measured by the single plate magnetometry method, the building factor was calculated using the following equation (1).

Building factor = W _17/50 (WM)/W _17/50 … (One)

Additionally, a three-phase model transformer for a transformer was manufactured using a grain-oriented electrical steel sheet that had been irradiated with an electron beam as described above. This model transformer was excited in a soundproof room under conditions of maximum magnetic flux density Bm = 1.7 T and frequency 50 Hz, and the noise level (dBA) was measured using a sound level meter.

In addition, in the same manner as above, a portion of the steel strip was cut out, and the strain distribution in the rolling direction around the thermal strain area introduced by electron beam irradiation was measured using a strain scanning method using high-intensity X-rays. As an example of such a strain distribution, a schematic diagram of a curve of the strain amount is shown in Figure 3.

As shown in the graph of the strain amount curve in FIG. 3, the strain distribution was such that two peaks were formed near the end of the thermal strain region. The average of the deformation amounts at both ends of the thermal deformation region (average deformation amount) was set to A, and the deformation amount at the center of the thermal deformation area was set to B, and the difference ΔAB (= A - B) of these deformation amounts was calculated. In addition, the relationship between material core loss W _17/50 , transformer noise level, and transformer building factor with respect to ΔAB was investigated.

In addition, the amount of deformation also shown in FIG. 3 can be calculated by the following equation when the d value of the reference point (non-strain point) is d0 and the d value of the measurement target point is d1. In other words, tensile strain is positive and compressive strain is additive.

{(d1 ― d0)/d0} × 100 (Unit: %)

The relationship between the difference in deformation amount ΔAB and the material core loss W _17/50 is shown in Figure 4, the relationship between the difference in deformation amount ΔAB and the transformer noise level is shown in Figure 5, and the relationship between the difference in deformation amount ΔAB and the transformer building factor is shown in Figure 6. .

Looking at FIG. 4, it can be seen that in the area where the difference in deformation amount ΔAB is positive (exceeding 0.000%), the change in W _17/50 is small. This is because this magnetic domain refinement promotes the magnetic domain refinement by blocking the flow of magnetic poles, and in the region where ΔAB is positive (exceeding 0.000%), the strain distribution in the thermal strain region does not have a significant adverse effect on the improvement of iron loss. I think it's because of this. On the other hand, when ΔAB entered the negative region, deterioration of core loss was confirmed. This is believed to be because as the total amount of strain increases, the hysteresis loss also increases.

Looking at FIG. 5, it can be seen that the transformer noise is suppressed in the area where the difference in deformation amount ΔAB is positive (exceeding 0.000%). This is thought to be because the total amount of strain in the thermal strain region decreased as the thermal strain for magnetic domain refinement became distributed concentrated at both ends.

Looking at Figure 6, it can be seen that as the difference in deformation amount ΔAB increases, the building factor tends to decrease. This is believed to be because the strain is concentrated in the region of the feedback domain end (II), thereby promoting the formation of the auxiliary magnetic domain described above, improving the rotational iron loss, and thus reducing the iron loss of the transformer.

From the above experimental results, in the strain distribution in the rolling direction of the thermal deformation region, the strain at both ends of the thermal deformation region is a tensile strain larger than the strain at the center of the thermal deformation region, that is, the In the region where ΔAB is positive (exceeding 0.000%), the noise and building factor of the transformer can be improved while maintaining the low core loss effect due to magnetic domain refinement. Moreover, when ΔAB is 0.040% or more and 0.200% or less, higher low noise is achieved. It has been proven that low-building factorization is effective.

That is, a linear thermal deformation region is formed in the direction transverse to the rolling direction, and within the thermal deformation region, a distribution in which greater tensile strain is formed at both ends of the rolling direction than at the center of the rolling direction is desirable. In particular, the thermal deformation region is preferable. When the difference ΔAB (= A - B) between the average amount of strain A at both ends and the amount of strain B at the center of the thermal strain region is 0.040% or more and 0.200% or less, a grain-oriented electrical steel sheet with higher transformer characteristics is obtained. I figured it out.

The present invention was completed through further examination based on this knowledge, and the main structure of the present invention is as follows.

1. A grain-oriented electrical steel sheet having a thermal deformation zone extending linearly in a direction transverse to the rolling direction,

In the strain distribution in the rolling direction of the thermal deformation region, the strain at both ends of the thermal deformation region is a tensile strain greater than the strain at the center of the thermal deformation region.

2. In the strain distribution in the rolling direction of the thermal deformation area, ΔAB (= A - B) is the difference between the average amount of strain A at both ends of the heat deformation area and the amount of deformation B at the center of the heat deformation area. The grain-oriented electrical steel sheet according to 1 above, wherein the content is 0.040% or more and 0.200% or less.

3. The grain-oriented electrical steel sheet according to 2 above, wherein the ΔAB is 0.050% or more and 0.150% or less.

According to the present invention, it is possible to obtain a grain-oriented electrical steel sheet that reduces energy loss and noise of a transformer.

Figure 1 is a schematic diagram showing candidates for points at which magnetic domains with magnetization components in a different direction from the rolling direction are formed in a steel sheet material subjected to non-heat-resistant magnetic domain refinement used in the examination leading up to the present invention.
Figure 2 is a schematic diagram showing an example of a ring-shaped beam profile.
Figure 3 is a schematic diagram showing an example of strain distribution in the thermal strain region of the grain-oriented electrical steel sheet of the present invention.
Figure 4 is a diagram showing the relationship between the difference in deformation amount ΔAB (=A - B) and the material iron loss W _17/50 .
Figure 5 is a diagram showing the relationship between the difference in deformation amount ΔAB (=A - B) and the transformer noise level.
Figure 6 is a diagram showing the relationship between the difference in deformation amount ΔAB (=A - B) and the transformer building factor.

(Grain-oriented electrical steel sheet)

Hereinafter, preferred embodiments of the present invention will be described in detail.

＜Component composition of grain-oriented electrical steel sheet＞

The composition of the grain-oriented electrical steel sheet of the present invention or the slab from which it is made may be any composition that allows secondary recrystallization to occur. Also, when using an inhibitor, for example, if an AlN-based inhibitor is used, Al and N may be contained in an appropriate amount, and if a MnS·MnSe-based inhibitor is used, Mn, Se and/or S may be added. Just add it in an appropriate amount. Of course, both the AlN-based inhibitor and the MnS·MnSe-based inhibitor may be used together.

When using the above inhibitor, the preferred contents of Al, N, S, and Se in the grain-oriented electrical steel sheet or the slab used as its material are, respectively,

Al: 0.010 to 0.065 mass%,

N: 0.0050 to 0.0120 mass%,

S: 0.005 to 0.030 mass%, and

Se: 0.005 to 0.030 mass%.

Additionally, the present invention can be applied to grain-oriented electrical steel sheets that do not use inhibitors and have limited Al, N, S, and Se contents. In this case, the contents of Al, N, S, and Se in the grain-oriented electrical steel sheet or the slab used as its material are, respectively,

Al: less than 0.010% by mass,

N: less than 0.0050% by mass,

S: less than 0.0050% by mass, and

Se: It is desirable to suppress it to less than 0.0050 mass%.

Next, the basic components and optionally added components of the grain-oriented electrical steel sheet of the present invention or the slab used as its material will be described in more detail.

C: 0.08 mass% or less

C is one of the basic ingredients, and is added to improve the structure of hot-rolled sheet. However, if the C content exceeds 0.08 mass%, it becomes difficult to decarburize during the manufacturing process up to 50 mass ppm or less, at which self-aging does not occur. , the C content is preferably 0.08% by mass or less. In addition, since secondary recrystallization can occur even in steel materials that do not contain C, there is no need to specifically set the lower limit of the C content. Therefore, the C content may be 0 mass%.

Si: 2.0 to 8.0 mass%

Si is one of the basic components and is an element effective in increasing the electrical resistance of steel and improving iron loss. To that end, it is desirable to set the content to 2.0% by mass or more. On the other hand, if the content exceeds 8.0 mass%, in addition to deterioration of processability and plateability, the magnetic flux density may also decrease. Therefore, it is preferable that the Si content is 8.0 mass% or less. Additionally, the Si content is more preferably 2.5% by mass or more, and more preferably 7.0% by mass or less.

Mn: 0.005 to 1.0 mass%

Mn is one of the basic components and is a necessary element to improve hot workability. To that end, it is desirable to set the content to 0.005% by mass or more. On the other hand, if the content exceeds 1.0 mass%, the magnetic flux density may deteriorate, so it is preferable that the Mn content is 1.0 mass% or less. Additionally, the Mn content is more preferably 0.01% by mass or more, and more preferably 0.9% by mass or less.

In the present invention, in addition to the above basic components, Ni, Sn, Sb, Cu, P, Mo, and Cr can be appropriately used as optional additive components known to be effective in improving magnetic properties.

In other words, the grain-oriented electrical steel sheet or the slab from which it is made,

Ni: 0.03 to 1.50 mass%,

Sn: 0.01 to 1.50 mass%,

Sb: 0.005 to 1.50 mass%,

Cu: 0.03 to 3.0 mass%,

P: 0.03 to 0.50 mass%,

Mo: 0.005 to 0.10 mass%, and

Cr: It can preferably contain one or more types selected from 0.03 to 1.50 mass%.

Among the above optionally added components, Ni is an element effective for improving the structure of a hot-rolled sheet and improving magnetic properties. If the Ni content is less than 0.03% by mass, the contribution to the magnetic properties is small. On the other hand, if it exceeds 1.50 mass%, secondary recrystallization may become unstable and magnetic properties may deteriorate. Therefore, the Ni content is preferably in the range of 0.03 to 1.50 mass%.

In addition, among the above optionally added components, Sn, Sb, Cu, P, Mo, and Cr are elements that improve magnetic properties in the same way as Ni. In both cases, if the content is less than the above lower limit, the effect is not sufficient, and if it exceeds the above upper limit, the growth of secondary recrystallized grains is suppressed, so the magnetic properties may deteriorate. Therefore, it is preferable that the contents of Sn, Sb, Cu, P, Mo, and Cr are each within the above range.

In addition, the remainder other than the above components is Fe and inevitable impurities.

Here, among the above components, C is decarburized in primary recrystallization annealing, and Al, N, S, and Se are purified in secondary recrystallization annealing. Therefore, the content of these components can be reduced to the level of unavoidable impurities in the steel sheet (grain-oriented electrical steel sheet as a final product) after secondary recrystallization annealing.

＜Manufacture of grain-oriented electrical steel sheet (until formation of heat distortion zone)＞

The grain-oriented electrical steel sheet of the present invention can be manufactured by the following procedures until the thermal strain region is formed.

That is, after hot rolling is performed on the steel material (slab) of the grain-oriented electrical steel sheet composed of the above composition system, hot-rolled sheet annealing is performed as necessary. Next, one cold rolling or two or more cold rollings with intermediate annealing in between are performed to finish the steel strip with the final thickness. Thereafter, the steel strip is subjected to decarburization annealing, an annealing separator containing MgO as the main component is applied, and then wound into a coil and subjected to final annealing for the purpose of secondary recrystallization and formation of a forsterite film. . If necessary, the steel strip after such final annealing is subjected to flattening annealing, and an insulating film (for example, a magnesium phosphate-based tension film) is additionally formed. In this way, a grain-oriented electrical steel sheet before forming a heat deformation region can be obtained.

＜Formation of heat deformation zone＞

Subsequently, a thermal deformation region is formed in this grain-oriented electrical steel sheet. The thermal deformation region can be formed by non-heat-resistant magnetic domain refinement, which is one of magnetization refinements. In this non-heat-resistant magnetic domain refinement, thermal strain can be locally introduced (forming a thermal strain region) by, for example, irradiating an energy beam to the surface of the steel sheet after the final annealing or after the formation of the insulating film. .

· Energy beam irradiation method

In forming the thermal strain region, the strain distribution according to the present invention can be formed more effectively by using an energy beam with a circular (ring-shaped) intensity distribution as seen in a ring mode laser system.

Beam sources of energy beams include lasers and electron beams, and any of these can be used to obtain the desired strain distribution. At that time, when using a laser, a ring mode laser system may be adopted, and when using an electron beam, a circular (ring-shaped) convex portion may be formed on the surface of the cathode. With these, the strain distribution according to the present invention can be formed.

· Direction of energy beam irradiation

In the production of the grain-oriented electrical steel sheet of the present invention, the thermal strain region can be formed in a linear shape on the steel sheet by irradiation of an energy beam such as the electron beam described above.

Specifically, linear thermal strain is introduced (formation of a thermal strain region) using one or more electron guns while irradiating a beam so that it intersects the rolling direction. At this time, the scanning direction of the beam is preferably in a direction within the range of 60° to 120° with respect to the rolling direction, and among these, it is set in a direction of 90° with respect to the rolling direction, that is, along the sheet width direction. Injection is more preferable. This is because as the deviation from the sheet width direction increases, the amount of strain introduced into the steel sheet increases, resulting in deterioration of magnetostriction.

In addition, the irradiation form of the energy beam may be irradiation continuously along the scanning direction (continuous linear irradiation) as long as the other requirements of the present invention are satisfied, or irradiation may be performed by repeating rectification and movement (dot dot irradiation). You can continue with the above investigation). Regardless of the irradiation type, the improvement effect of the present invention is obtained for building factor and magnetostriction, respectively.

In addition, both the continuous line shape and the dot shape are one aspect of “line shape.”

Hereinafter, preferred conditions for irradiating electron beams in manufacturing the grain-oriented electrical steel sheet of the present invention will be described in more detail.

· Acceleration voltage: 60 kV or more and 300 kV or less

A higher acceleration voltage is preferable because the straight-line propagation of electrons increases and the thermal influence on the outside of the electron beam irradiation point decreases. For this reason, it is preferable that the acceleration voltage is 60 kV or more. More preferably, it is 90 kV or more, and it is even better if it is 120 kV or more.

On the other hand, if the acceleration voltage is made too high, it becomes difficult to shield X-rays generated along with electron beam irradiation. Therefore, it is preferable that the acceleration voltage is 300 kV or less from a practical viewpoint. More preferably, it is 200 kV or less.

· Spot diameter (beam diameter): 300 ㎛ or less

The smaller the spot diameter, the more preferable it is because strain can be introduced locally. Therefore, it is desirable that the spot diameter (beam diameter) of the electron beam is 300 μm or less. Moreover, the spot diameter (beam diameter) of the electron beam is more preferably 280 μm or less, and even more preferably 260 μm or less. In addition, the spot diameter refers to the full width at half maximum of the beam profile acquired by the slit method using a slit with a width of 30 μm.

· Beam current: 0.5 ㎃ or more and 40 ㎃ or less

It is preferable that the beam current is smaller from the viewpoint of the beam diameter. This is because when the current is increased, the beam diameter is likely to expand due to Coulomb repulsion. Therefore, it is preferable that the beam current is 40 mA or less. On the one hand, if the beam current is too small, there is insufficient energy to form deformation. Therefore, it is preferable that the beam current is 0.5 mA or more.

· Electron beam output: 300 W or more and 4000 W or less

The electron beam output is calculated as the product of the acceleration voltage and beam current. It is preferable that the electron beam output is smaller from the viewpoint of the amount of introduced strain. This is because when the electron beam output is increased, the amount of strain introduced becomes excessive, causing deterioration of hysteresis loss and noise beyond the improvement of eddy current loss. Therefore, under the condition that the acceleration voltage and beam current satisfy the above preferred ranges, the electron beam output is preferably set to 4000 W or less. On the one hand, if the electron beam output is too small, there is insufficient energy to form strain. Therefore, it is desirable that the electron beam output is 300 W or more.

· Vacuum degree of beam irradiation environment

The electron beam is scattered by gas molecules, causing an increase in beam diameter or halo diameter, and a decrease in energy. Therefore, the degree of vacuum in the beam irradiation environment is preferably higher, and the pressure is preferably set to 3 Pa or less. There is no particular restriction on the lower limit, but if it is excessively reduced, costs related to vacuum systems such as vacuum pumps increase. Therefore, for practical purposes, the degree of vacuum in the beam irradiation environment is preferably set to 10 ^-5 Pa or more.

In addition, conditions for laser irradiation in manufacturing the grain-oriented electrical steel sheet of the present invention will be explained in more detail.

· Laser output: 20 W or more and 500 W or less

It is preferable that the laser output is smaller from the viewpoint of the amount of introduced strain. This is because when the laser output is increased, the amount of strain introduced becomes excessive, causing deterioration of hysteresis loss and noise beyond the improvement of eddy current loss. Therefore, it is preferable that the laser output is 500 W or less. On the one hand, if the laser power is too small, there is insufficient energy to form deformation. Therefore, it is preferable that the laser output is 20 W or more.

＜Deformation characteristics in grain-oriented electrical steel sheets＞

· Strain distribution

The strain distribution in the rolling direction of the thermal strain region on the surface of the steel sheet can be measured by the EBSD-Wilkinson method. In this EBSD-Wilkinson method, for example, an electron beam is irradiated to the surface of a steel sheet, a Kikuchi pattern is acquired for each measurement point, the strain-free point is used as a reference point, and analysis software such as CrossCourt is used to determine the The amount of deformation is calculated from the amount of deformation of the Kikuchi pattern.

Here, the thermal deformation region in the present invention refers to the same region as the linear closure magnetic domain region formed by an energy beam irradiated in a linear form to the steel sheet. In addition, the length of the looping magnetic domain formed on the surface of the steel sheet in the rolling direction (same as the length of the thermal deformation region) can be measured by acquiring the magnetic domain pattern on the surface of the steel sheet using a commercially available domain viewer.

· Average deformation amount A and deformation amount B

Using the above measurement method, the strain distribution in the rolling direction of the thermal deformation region on the surface of the steel sheet is measured, the average amount of strain at both ends of the thermal deformation region in the rolling direction is set to A, and the average amount of deformation at both ends of the thermal deformation region in the rolling direction is set to A, and Let the amount of deformation be B. Additionally, the amount of deformation at both ends of the rolling direction may be the same or different.

At this time, if the difference ΔAB (A - B) between A and B is positive (more than 0.000%), the effect of the present invention is obtained, and if it is 0.040% or more and 0.200% or less, a grain-oriented electrical steel sheet with higher properties is obtained. obtained. Moreover, ΔAB is more preferably in the range of 0.050% or more and 0.160% or less.

Example

Next, the present invention will be explained based on examples. The following examples show preferred examples of the present invention and are not limited in any way by these examples. In addition, it is possible to add and implement changes within the scope suitable for the purpose of the present invention, and it goes without saying that even such aspects can be included in the technical scope of the present invention.

In this example, as a material for the grain-oriented electrical steel sheet, a slab containing the components shown in Table 1, with the remainder being Fe and inevitable impurities, was used. For this slab, hot rolling, hot-rolled sheet annealing, one cold rolling, decarburization annealing, application of an annealing separator, and final annealing are performed in this order under prescribed conditions, respectively, to obtain a steel strip of grain-oriented electrical steel sheet with a sheet thickness of 0.23 mm. got it

The steel strip of the grain-oriented electrical steel sheet was used as a test material, and an energy beam was irradiated to this test material. At this time, either a laser or an electron beam was used as the beam source of the energy beam (as shown in Table 2), and irradiation was performed in either a continuous line or dot form (as shown in Table 2). In this way, a thermal deformation region was formed on the surface of the grain-oriented electrical steel strip (magnetic domain refinement treatment). Here, dot-shaped irradiation refers to an irradiation form in which energy beam irradiation is performed by repeating rectification and movement in the scanning direction.

The energy beam irradiation conditions for both laser and electron beams are irradiation direction: approximately 90° to the rolling direction, beam output: 0.6 to 6 kW (acceleration voltage: 60 to 150 kV, beam current: 1 to 40 mA). Also, in the case of electron beam, the vacuum degree of the beam irradiation environment was set to 0.3 Pa. The profile of the irradiating beam was all ring-shaped, and a beam with a beam diameter of 200 ㎛ was used. At this time, in order to change the values of the average deformation amount A, deformation amount B, and ΔAB, in addition to the beam output, conditions such as the energy difference between the energy maximum value in the ring-shaped profile and the energy minimum value at the center of the profile, and the distance between the energy maximum values, etc. Beam irradiation was performed by adjusting the beam irradiation.

A portion of the grain-oriented electrical steel strip in which the thermal strain region was formed in this way was cut out, and the magnetic flux density (B ₈ ) and iron loss (material iron loss: W _17/50 ) were measured as magnetic properties using the single sheet magnetic measurement method described in JIS C2556. did. Additionally, a three-phase laminated transformer (iron core mass 500 kg) is manufactured from the above steel strip, and at a frequency of 50 Hz, the iron loss when the magnetic flux density of the iron core leg portion is 1.7 T (transformer iron loss: W _17/50 (WM) ) was measured. The transformer iron loss W _17/50 (WM) at 1.7 T and 50 Hz was taken as the no-load loss measured using a watt meter. From this value of W _17/50 (WM) and the value of W _17/50 measured by the single plate magnetometry method, the building factor (BF) was calculated using the following equation (1). The results are shown in Table 2.

Building factor = W _17/50 (WM)/W _17/50 … (One)

Additionally, a three-phase model transformer for a transformer was manufactured using a grain-oriented electrical steel sheet subjected to magnetic domain refining treatment as described above. This model transformer was excited in a soundproof room under conditions of maximum magnetic flux density Bm = 1.7 T and frequency 50 Hz, and the noise level (dBA) was measured using a sound level meter. The results are shown in Table 2.

In addition, in the same manner as above, a part of the steel strip was cut out, and the strain distribution in the rolling direction around the thermal deformation area was measured using the EBSD-Wilkinson method. In addition, using a commercially available domain viewer (MV-95 manufactured by Sigma High Chemicals), the length in the rolling direction (same as the length of the thermal deformation region) of the closure domain formed on the surface of the steel sheet was measured. Then, the average of the amount of deformation at both ends of the thermal deformation region (average amount of deformation) was set to A, and the amount of deformation at the center of the thermal deformation area was set to B, and the difference ΔAB (= A - B) of these deformations was calculated. In addition, tensile strain was assumed to be positive and compressive strain was assumed to be negative. These values are shown in Table 2.

From Table 2, compared to Nos. 37 to 40 where ΔAB is negative, under the conditions of Nos. 2 to 9, 11 to 18, 20 to 27, and 29 to 36 where ΔAB is positive (exceeding 0.000%), the beam source of the energy beam, Regardless of the survey format, the low noise and low building factor effects can be confirmed. In particular, a high effect is seen under conditions where ΔAB is 0.040% or more and 0.200% or less. Additionally, under conditions where ΔAB is 0.050% or more and 0.150% or less, an even higher effect is observed.

Claims (3)

A grain-oriented electrical steel sheet having a thermal strain zone extending linearly in a direction transverse to the rolling direction,
In the strain distribution in the rolling direction of the thermal deformation region, the strain at both ends of the thermal deformation region is a tensile strain greater than the strain at the center of the thermal deformation region. According to claim 1,
In the strain distribution in the rolling direction of the thermal deformation zone, ΔAB (= A - B), which is the difference between the average strain amount A at both ends of the heat deformation zone and the strain B at the center of the heat deformation zone, is 0.040%. Grain-oriented electrical steel sheet of 0.200% or less. According to claim 2,
A grain-oriented electrical steel sheet wherein the ΔAB is 0.050% or more and 0.150% or less.

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